[Bug Report] iphone safari在当前页面跳转第三方网站后点击返回到页面x-input value丢失

### VUX version
2.9.0

### OS/Browsers version
iphone6sp、safari

### Vue version
2.5.16

### Code

```html
test.vue
---------------------------start-----------------------------------

import { XInput, Group } from "vux";
export default {
components: {
XInput,
Group
},
data() {
return {
name:'test'
};
},
mounted() {},
methods: {}
};

------------------------------end--------------------------------
```

### Steps to reproduce
点击访问百度，点击safari虚拟返回键，x-ipnut value丢失、input value存在

### What is Expected?
x-ipnut value保留

### What is actually happening?
x-ipnut value丢失